Alloy for dental amalgam

ABSTRACT

The alloy 26 percent Sn, 8-10 percent Au and Ag qs to 100 percent, on mixing with mercury, forms an amalgam particularly suitable for dental use.

D United States Patent 1 1111 3,762,917

Johnson, Jr. 1 Oct. 2, 1973 [54] ALLOY FOR DENTAL AMALGAM 2,27l,264l/l942 Kaufmann ct a1. 75/lb9 48 ,280 11 1892 .l" b k 7 lo) [76]Inventor: Lewis B. Johnson, Jr., Univers1ty of 225399] 541942 ggs g zi 4C V1rglma,T1}0mI0" Hall, 3,141,761 7/1964 Riihm 75 173 R Cha 229013,305,356 2/l967 Youdelis 75 173 c [22] Filed: July 6, B71

Primary Examinerl3. Dewayne Rutledge [2n 160308 Assistant ExaminerE. L.Weise Altorney -Harold T. Stowell et al. [52] US. Cl. 75/169, 75/173 R[51] Int. Cl. C22c 7/00 [58] Field of Search 75/l73 R, 173 C, ABSTRACT75/169 The alloy 26 percent Sn, 8-10 percent Au and Ag qs 1561 2159253172653 23132633525557;

UNITED STATES PATENTS g P y 3 Claims, No Drawings 249,880 ll/l88lBonwill ..75/169 ALLOY FOR DENTAL AMALGAM This invention relates to anovel alloy particularly intended for use in dental amalgams.

Dental amalgams are unique materials prepared according to ratherdetailed and strict specifications. Conventional alloys for dentalamalgam use contain 68-70 percent silver and about 25 percent tin withthe balance mainly cooper. When the alloy (essentially Ag Sn) istriturated with about 50 percent by weight of mercury, the settingreaction results in the formation of two phases, Ag l-lg and Sn,Hg;excess Ag Sn remains embedded as particles in a matrix of these twophases.

It has now been found that the second or Sn Hg phase is relatively weakand is the phase most subject to destructive corrosion. Based on theseconsiderations, it would appear desirable to eliminate the Sn Hg phasefrom dental amalgams. However, the presence of tin, which acceleratesthe rate of amalgamation and reduces expansion on setting, also appearsdesirable.

I have discovered that the second or Sn l-lg phase can be eliminated,tin retained and an improved singlephase matrix, non-expanding dentalamalgam prepared from the novel alloy 26 percent Sn, 8-10 percent Au andAg qs to 100 percent. Alloys containing lesser amounts of gold areineffective to bring about the diffusion of tin and mercury necessary toform a singlephase matrix. Alloys containing greater amounts of goldyield amalgams exceeding American Dental Association specifications formaximum permissible expansion and lessened ultimate tensile strength.

In addition to containing the optimum amount of gold indicated above,the alloy must be prepared by a quick-cooling or quenching procedure.Alloys prepared in the conventional way by slow cooling from the melt donot form a single-phase matrix. It appears that quick cooling isrequired to produce an alloy structure capable of effecting thesubsequent diffusion of tin and mercury necessary forsingle-phaseformation.

Dental amalgams prepared from alloys according to the present invention,in addition to forming a strong single-phase, non-expanding matrix, arehighly corrosion resistant and exhibit little creep or flow. Myinvention is further illustrated by means of the following nonlimitingexamples:

An alloy mixture containing 10 percent Au, 64 percent Ag and 26 percentSn, all by weight was spray cooled from the melt. Amalgams were preparedfrom this alloy by conventional techniques, i.e., trituration with about50 percent by weight of mercury. X-ray diffraction patterns of theamalgam taken after 1 hour showed a peak corresponding to the second orSn l-lg phase but much smaller than that obtained with conventionalamalgam. X-ray patterns: taken after storage at body temperature for 14days showed peaks attributable only to the first phase; the second orSn-,Hg phase was no longer present.

An alloy having the same gross composition was prepared as an ingot fromthe melt. Powder was milled from the ingot, balled milled and made intoan amalgam with 50 percent by weight of mercury. The amal gam did notform a single-phase matrix.

Corrosion tests were run on amalgams made from the spray cooled alloypowder of the invention at O.25 volt, plotting time against the currentrequired for corrosion. Comparable tests were run on conventionalamalgams. The amalgam of the present invention was much more noble after1 hour and the dissolution of specimens aged at body temperature for 14days was virtually negligible.

Tensile strength tests were run on amalgams made from the spray driedalloy powder of the invention and on conventional amalgams. The presentalloys, after setting several days, had tensile strengths of8,000-l0,000 p.s.i., roughly l0-30 percent greater than the conventionalamalgam controls. The average value of creep for 5 samples was about0.94 percent compared to values of about 1.0-1.7 percent forconventional amalgam controls.

I claim:

1. An alloy consisting essentially of 26 percent Sn, 8-l0% Au and Ag qsto percent quick-cooled from the melt.

2. A method for preparing an alloy adapted for use in dental amalgamswhich comprises spray drying a molten mixture consisting essentially of26 percent Sn, 8-10 percent Au and Ag qs to 100 percent.

3. A dental amalgam prepared by triturating an alloy consistingessentially of 26 percent Sn, 8-10 percent Au and Ag gs to 100% withabout 50 percent of mercury by weight of the alloy, said alloy havingbeen quick-cooled from its melt.

2. A method for preparing an alloy adapted for use in dental amalgamswhich comprises spray drying a molten mixture consisting essentially of26 percent Sn, 8-10 percent Au and Ag qs to 100 percent.
 3. A dentalamalgam prepared by triturating an alloy consisting essentially of 26percent Sn, 8-10 percent Au and Ag gs to 100% with about 50 percent ofmercury by weight of the alloy, said alloy having been quick-cooled fromits melt.